What Is Overmolding, And Why Should You Use It?

Overmolding is an injection molding process used in many industrial capabilities. It is an integral part of prototyping and custom production, where it is essential in the overlay of plastics (plastic overmolding) and metals.

In this article, you’ll know more about the overmolding process. This will involve how the process works, the materials, and how it is used. When you finish the article, you will know a lot about the process. Let’s get right on it.

What Is Overmolding Process?
The overmolding injection molding process involves creating a single material by combining two or more materials through molding. The material can be the same or different type.

Proper understanding of the overmolding injection molding process comes with understanding the two types of materials utilized in the process. These materials are the substrate and the overmold.

What Is An Overmold And Substrate?
The overmold is the type of material molded on the substrate, while the substrate is the primary material. There can be two or more overmold based on the end-product and the manufacturer’s innovation.

How Overmolding Process Works?
To understanding the plastic overmolding process, you need to know the three basic categories. Below are the three sorts of overmolding.

Insert Molding

  • In rigid molding plastic or soft elastomers, insert molding is the ideal sort of overmolding since it is economical and easy than the other. In insert molding, the hard segments are initially separated into tools before the soft materials’ ejection.
  • It additionally involves the usage of elastomers as an adhesion bond. This can be in the form of chemicals, mechanical locks, etc. For chemical adhesion to occur, you should heat the elastomer at the right temperature. This will require you to heat the hard segment’s surface.

Two-Shot Molding

  • Instead of the insert molding, the two-shot molding needs you to utilize two injection molding machines. You can inject the hard segment-first, following the elastomeric mold into the injection molding machine.
  • The heated substrate utilized is always in a gel state or semi-solid. The mold’s design will be modeled to project the indirect part of the hard segment on the substrate. The 2-shot overmolding injection molding process is ideal for those who value stable mechanical bonds.

Co-Injection Molding

  • Of the three different types of overmolding, co-injection molding is the most expensive and difficult to control. Its process is additionally different since it demands the injection of the substrate and the elastomer into the same mold. The materials should also be compatible.
  • In regards to the quality overmolding, co-injection is the ideal choice. This is due to all the materials are in the same molten state.

Materials Commonly Utilized In Overmolding
Overmolding can be utilized with a wide range of materials, including:

  • ABS (Acrylonitrile Butadiene Styrene)
  • HDPE (High-density Polyethylene)
  • PEEK (Polyether Ether Ketone)
  • Nylon (Polyamide)
  • PC (Polycarbonate)
  • PE (Polyethylene)
  • PEI (Polyetherimide)
  • PBTR (Polybutylene Terephthalate)
  • PMMA (Acrylic)
  • POM (Polyoxymethylene)
  • PP (Polypropylene)
  • SI (Silicone)
  • TPE (Thermoplastic Elastomers)
  • TPU (Thermoplastic Polyurethane)
  • TPR (Thermoplastic Rubber)

What Is Overmolding Used For?

The overmolding process is utilized for many reasons that vary as per the characteristics of a particular project. Some common materials include toothbrushes, tool handgrips (e.g., cordless drills and screwdrivers), and personal care products (e.g., shaving razors and shampoo bottles).
Here are some examples of regular overmolding applications:

  • Rubber Over Plastic – A rigid plastic substrate is first molded. Afterward, soft rubber or TPE is molded onto or around the substrate. This is frequently utilized to give a soft grip area to a rigid part.
  • Plastic Over Plastic – Here, a rigid plastic substrate is first molded. Then different rigid plastic is molded onto or around the substrate. The plastics can vary in color and/or resin.
  • Plastic Over Metal – A metal substrate is here machined, formed, or cast. Then, the substrate is entered into an injection molding tool, and the plastic is molded around the metal. This is usually utilized to capture metal elements in a plastic part.
  • Rubber Over Metal – A metal substrate is a cast, formed, or machined. After then, the substrate is inserted into an injection molding tool, and the rubber or TPE is molded onto or around the metal. This is often used to provide a soft-grip surface.


Things to consider:

  • There are many compatibility issues and limitations to note between different types of materials.
  • You aren’t limited to just two materials. At Truventor, we have made some products with three different types of materials on one part to accomplish color breaks and grip surfaces. Here is a simple instance with a product you’ll be intimately familiar with: scissors.

Advantages of Using Overmolding Process
Manufacturers who want to add a soft-touch exterior to their products that enhance grip or “feel” and provide a stylish appearance attractive to consumers are prime candidates for overmolding. Overmolding also reduces shock and vibration, dampens sound, provides electrical insulation, and improves chemical/UV resistance, increasing product longevity. Overmolding also lowers production costs despite improving product viability and customer satisfaction. Below are the advantages of using overmolding.

  • Better Product Performance
  • Increased Shelf Appeal
  • Lower Production Cost

How to Know If Overmolding Is Better for Your Project?
Below is a guide to decide which manufacturing process is ideal for your project:

Select overmolding when:

  • Your finished piece can be made of rubber and/or thermoplastics.
  • Your finished design comprises multiple layers, materials, and/or colors.
  • You will be manufacturing both the substrate and lower layer.
  • Your finished piece won’t need to be taken apart or disassembled.

Select insert molding when:

  • You are utilizing a prefabricated substrate.
  • Your substrate is made of wires, metal, or computerized parts.
  • You’re looking for the finished part to be one solid piece.

Collaborating with an experienced custom injection molder — especially one with scientific molding expertise, like Truventor — will assist you with navigating the pros and cons of utilizing overmolding on your project and guide you with the right decision for your project, your application, and bottom line.

To learn more about how overmolding can improve performance and aesthetics while lowering production costs, get in touch with our experts today!

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